Process of rolling rails



Patented Jan. 12, 1937 UNITED STATES PTET DFFIQE PROCESS OF ROLLINGRAILS Pennsylvania No Drawing. Application July 16, 1934, Serial No.735,429

10 Claims.

My invention relates to the rolling of rails and particularly to therolling of heavy section rails used in main line steam railway service.

The object of the invention is to provide a rolling process which willeliminate or avoid the formation of discontinuities in rails variouslyreferred to as flakes, checks or shatter cracks.

In the heads of rails, particularly in those of large cross sectionweighing 100 pounds per yard or more in which a relatively high carbonor high manganese steel is used, it is common to find numerous cracks orchecks beneath the surface. These cracks rarely if ever extend to thesurface of the rail and in order to detect them it is nec essary tosection the rail head and generally to etch the surface of the section.However, they may appear occasionally on the fractured surfaces of railsbroken in the drop test as spots differing in color from the majorportion of the fracture and sometimes referred to as grey spots.

The greater number of. these shatter cracks are roughly circular andvary from pin head size to a half inch or more in diameter. Their widthis so slight that for all practical purposes the faces of the crack maybe considered to be in contact. The bright appearance of the crack faceswhich occasionally may be found on a rail fracture indicates that thecracks do not contain chemically active gases.

That shatter cracks are not of themselves as serious defects as theymight seem is attested by the fact that an appreciable percentage of therails which are in regular service contain them. They are recognized,however, as starting points for the dangerous type of fatigue failuresknown as transverse fissures and much effort has been devoted toeliminating them. It is generally accepted that shatter cracks form asthe rail cools from the rolling temperature and are due to stressesresulting from non-uniform expansion and contraction of the metal indifferent portions thereof. The steps heretofore taken to eliminate themhave therefore centered around controlled cooling of the rails and thedevelopment of steel for same, which has the maximum ductilityconsistent with the hardness required in the rail. To my knowledge,however, no rail manufacturer has succeeded in completely eliminatingshatter cracks by control of steel making practice, and the controlledcooling processes that have been proposed and used are somewhatcumbersome and expensive. Furthermore, a slow cooling process, if.effective in eliminating cracks, has a tendency to reduce the hardnessand strength of the rail below optimum values.

My invention comprises rolling standard rail ingots to blooms and,contrary to usual practice, in allowing the blooms to cool to below thetransformation range before rolling them to rails. Preferably they areallowed to cool to substantially atmospheric temperature.

Rail ingots are usually broken down to blooms of convenient size on onemill and the blooms subsequently rolled to finished rails on a secondmill. Heretofore, the blooms have either been transferred directly fromthe first mill to the second mill for final rolling, or if a highertemperature is required in the finishing mill, they are charged into areheating furnace as they come from the blooming mill and brought up tothe desired temperature. It has been found that a considerablepercentage of rails rolled in this manner contain the shatter cracksabove referred an ingot having a cross section of 23 by 28 inches,

and after stripping the ingot from the mold, charge it into a soakingpit in which its temperature is equalized to a suitable rollingtemperature, say 2200 F. I then roll the ingot to a bloom having a crosssection about 10 inches square,

and shear this into lengths from each of which a convenient multiple ofvthe length of a finished rail may be rolled. The blooms or billets thusproduced are allowed to cool before charging them into the reheatingfurnace. The rate of cooling and the minimum temperature reached may bevaried to suit the character of steel being used, and the convenience ofmill operations. My preferred practice is to pile the blooms in lifts ofconvenient size and thus to secure a considerably delayed cooling orpile anneal. When thus cooled in piles the blooms are allowed to reach atemperature of 400 F. or below. Ordinarily they are allowed to cool toatmospheric temperature, and they may, in fact, be kept in storage untilit is convenient to use them.

In a modification of the process the blooms may be held upon a hot bedas they come from the first mill until they have passed through thetransformation range, as indicated by their becoming magnetic and maythen be charged into the reheating furnace.

The subsequent operation in either case consists in reheating the bloomsto normal rolling temperature and rolling them to finished. railsection.

Various heat treatments have been proposed and used on finished rails toharden and toughen them, and these treatments may be used to advantageon rails rolled by my improved process. In fact, heat treatmentsinvolving drastic cooling of the rails are more practicable when appliedto the improved rails produced by my process than to rails made bystandard methods, and my invention contemplates the use of suchtreatments in combination with the improved rolling process.

The cooling of the blooms prior to final rolling undoubtedly tends tostabilize and refine the structure of the steel and to halt the growthof coarse crystals which takes place during the usual reheatingoperation. I have found that cracks may form in the blooms whilecooling, and it is possible that a certain amount of internal stress isthereby relieved. When such cracks occur, I have found that they aresatisfactorily welded shut in the subsequent rolling, if such rollinginvolves a reduction of about one and one half times the cross sectionalarea of the final product. However, I do not limit myself to any theorywhich would account for the improved condition of the rails rolled by myprocess.

From an operating standpoint it is sufficient to note that my processpractically eliminates the formation of shatter cracks and that theadded cost of heating cold blooms to rolling temperature is, in manycases, offset by the resulting independence of open hearth and rail milloperations. Thus by working the rail mill from a stock of cold blooms,it is no longer necessary to hamper open hearth-operations by thelimitations of the rail mill or vice versa. Furthermore, sound rails canbe produced without providing equipment for the controlled cooling ofthe finished rails, and the output of the mill can therefore be madeindependent of the capacity of any such equipment.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

l. The process of manufacturing rails substantially free from shattercracks which comprises rolling blooms, allowing said blooms to cool tobelow 400 degrees F., reheating said blooms and rolling rails therefrom.

2. The process of manufacturing rails substantially free from shattercracks which comprises rolling blooms, allowing said blooms to: cool tosubstantially atmospheric temperature, reheating said blooms and rollingrails therefrom.

3. In the manufacture of rails substantially free from shatter cracksthe steps of rolling an ingot to a billet having a cross sectional areaat least two and one half times that of the finished rail, allowing saidbillet to cool to below 400 degrees F., reheating said billet androlling it to the finished rail.

4. In the manufacture of rails substantially free from shatter cracksthe steps of rolling an ingot to a billet having a cross sectional areaat least two and one half times thatof the finished rail, allowing saidbillet to cool to substantially atmospheric temperature, reheating saidbillet and rolling it to the finished rail.

5. The process of manufacturing rails substantially free from shattercracks which comprises rolling blooms, allowing said blooms to cool tobelow 400 degrees F., reheating said blooms, rolling rails from saidblooms and allowing said rails to cool normally in the air.

6. The process of manufacturing rails substanr tially free from shattercracks which comprises rolling blooms, allowing said blooms to cool tosubstantially atmospheric temperature, reheating said blooms, rollingrails from said blooms and allowing said rails to cool normally in theair.

7. The process of manufacturing rails substantially free from shattercracks which comprises rolling blooms, allowing said blooms to cool to atemperature below the gamma-alpha transformation range, reheating saidblooms and rolling rails therefrom.

8. The process of manufacturing rails substantially free from shattercracks which comprises rolling blooms, forming piles of said bloomswhile above their transformation range, allowing said blooms in saidpiles to cool to below 400 degrees F., reheating said blooms and rollingrails therefrom.

9. The process of manufacturing rails substantially free from shattercracks which comprises rolling blooms, subjecting said blooms toretarded cooling to below 400 degrees F., reheating said blooms androlling rails therefrom.

10. The process of manufacturing hardened rails substantially free fromshatter cracks which comprises rolling blooms, cooling said blooms tobelow 400 degrees F., reheating said blooms, rolling said blooms torails, and hardening said rails by accelerated cooling.

ALBERT P. SPOONER.

